This invention relates to radio frequency (RF) communication systems, and more specifically to RF transceivers for RF communication systems.
Radio frequency communication systems are being widely used for wireless communications. As is well known to those having skill in the art, radio frequency communication systems include wireless communication terminals that communicate with one another and with wire telephone systems. Radio frequency communication systems include analog and digital cellular telephone systems, and satellite telephone systems. Wireless communications terminals include analog and digital cellular terminals, satellite terminals and multiple mode cellular/satellite terminals. These wireless communications terminals may be simple wireless radiotelephones. However, more sophisticated personal communications systems (PCS), that provide functions in addition to those of a telephone, such as facsimile, data communications, data processing, word processing and other personal communications systems functions are also included.
Wireless communication terminals continue to undergo miniaturization. At the same time, higher performance and longer battery life are also generally desirable. Accordingly, there continues to be a need for improved designs of RF transceivers that are used in wireless communication terminals. As is well known to those having skill in the art, a transceiver generally includes a transmitter and receiver to transmit communications via an antenna and to receive the communications from the antenna. The antenna may include multiple antenna elements.
FIG. 1 is a block diagram of a conventional RF transceiver. As shown in FIG. 1, the RF transceiver 100 receives a transmit signal F0 from a transmit circuit of a wireless communication terminal and transmits this signal to antenna 208. A received signal from antenna 208 is also provided to a receive circuit.
As also shown in FIG. 1, the transceiver includes an amplifier 202, an isolator 204 and a duplexer 206. As is well known to those having skill in the art, an isolator 204 is a device that permits radio frequency energy to pass in one direction indicated by the arrow in Block 204, while providing high isolation to reflected energy in the reverse direction. As is also known to those having skill in the art, an isolator may be produced using a microwave circulator with one port terminated in the characteristic impedance. Accordingly, ports 1 and 2 of isolator 204 couple amplifier 202 to transmit port (Tx) of duplexer 206. Port 3 of isolator 204 is terminated by a characteristic impedance R.
Duplexer 206 couples the transmit port Tx and receive port Rx to antenna 208 via antenna port Ant. As is well known to those having skill in the art, a duplexer is a radio frequency device that isolates a receiver from a transmitter while allowing them to share a common antenna. A duplexer generally includes a transmit filter and a receive filter that are coupled to an antenna input. The design of a conventional transceiver 100 and of individual blocks 202, 204, 206 and 208 are well known to those having skill in art and need not be described further herein.
The transmitter portion of a transceiver is often a large power consumer in a wireless communication terminal due to the need to transmit RF communications with sufficient power to be received properly. Moreover, the RF transmitter may degrade performance of the wireless communication terminal due to the introduction of noise in the transmitted signal. Accordingly, there continues to be a need for improved RF transceivers, and more specifically RF transmitters therefor.
It is therefore an object of the present invention to provide improved radio frequency (RF) transceivers and wireless communication terminals including the same.
It is another object of the present invention to provide RF transceivers and wireless communication terminals that can operate with reduced power and can produce lower noise.
These and other objects are provided according to the present invention, by an RF transceiver that includes a transmit chain that transmits a transmit signal to an antenna and a receive chain that generates a receive signal from the antenna, wherein the receive chain includes a duplexer and the transmit chain is free of a duplexer. By removing the duplexer from the transmit chain, power losses incurred by the duplexer may be reduced and preferably eliminated from the transmit chain.
More specifically, an RF transceiver according to the present invention comprises a circulator including first, second and third circulator ports, that circulates power from the first circulator port to the second circulator port, to the third circulator port and then to the first circulator port. A transmit signal is coupled to the first circulator port, preferably via at least one amplifier. An antenna is coupled to the second circulator port. A duplexer is coupled to the third circulator port and generates a receive signal. Accordingly, the combination of a circulator in the transmit chain and a duplexer in the receive chain can reduce the power losses in the transmit chain.
According to another aspect of the present invention, noise may be reduced by replacing the amplifier with first and second amplifiers and a bandpass filter therebetween. The first amplifier is coupled to the transmit signal and the second amplifier is coupled to the first circulator port of the circulator. By providing a bandpass filter between the first and second amplifiers, lower noise may be obtained while still maintaining the same gain.
In a preferred embodiment of the present invention, the duplexer includes an antenna port, a transmit port and a receive port. The third circulator port is coupled to the antenna port, and the receive port accepts the receive signal. An impedance matching resistor is coupled to the transmit port in order to dissipate power that is reflected from the antenna.
Radio frequency transceivers according to the present invention may be used in a wireless communication terminal that includes a transmit circuit, a receive circuit, a user interface and a controller that is coupled to the user interface, the transmit circuit and the receive circuit. The RF transceiver includes an amplifier that is coupled between the transmit circuit and the first circulator port, an antenna that is coupled to the second circulator port, and a duplexer that is coupled between the third circulator port and the receive circuit. Accordingly, high gain, low noise transceivers may be provided.